Method of cleaning printed circuit boards with dimethylcyclooctadienes

ABSTRACT

A cleaning composition which comprises dimethylcyclooctadienes is disclosed. There is further disclosed a method of cleaning printed circuit boards or printed wiring boards, which comprises: contacting the board with a composition comprising dimethylcyclooctadienes and 2-20% by weight of a surfactant; rinsing the board with water; and drying the board.

This is a Rule 60 Divisional of Ser. No. 07/578,301 filed Sep. 5, 1990U.S. Pat. No. 5,132,039.

This invention relates to a novel cleaning composition and applicationthereof, and more particularly it relates to a cleaning compositionsuitable for use in cleaning printed circuit or printed wiring boards toremove soldering fluxes therefrom during the fabrication of the boards.

There have recently been proposed a variety of cleaning compositionswhich contain terpenes of eight carbons. For instance, a water basedcleaning composition is disclosed in Japanese Patent Laid-open No.54-14406. The composition contains d-limonene and surfactants, and isalleged to be useful to clean, for example, carpets or glass. Similarcompositions which contain limonenes or pinenes as effective ingredientsare also disclosed in Japanese Patent Laid-open Nos. 61-157596 and61-183398.

Meanwhile, halogenated aliphatic hydrocarbons have been widely used aseffective ingredients in cleaning compositions for industrial use, inparticular, for removal of soldering fluxes in the fabrication ofprinted circuit or printed wiring boards.

In general, the soldering fluxes fall into two broad categories: watersoluble fluxes and rosin fluxes. The water soluble fluxes usuallycontain strong acids and/or amine hydrohalides and are accordinglycorrosive. Thus, if traces of residues remain on boards, prematurecircuit failure will result. For that reason, rosin fluxes are preferredin the fields where high durability or precision is required.

The rosin fluxes are non-corrosive. However, traces of residual rosinfluxes should be also removed carefully to prevent premature circuitfailure on account of decreased board resistance. The water solublefluxes may be readily removed from printed circuit boards with warm soapwater, while halogenated aliphatic hydrocarbons such as1,1,1-trichloroethane, trichlorofluoromethane, trichlorotrifluoroethaneor mixtures of these have been heretofore used to remove the rosinfluxes from printed circuit boards following soldering.

However, the use of such halogenated hydrocarbons is causing a seriousglobal environmental problem of ozone layer destruction, and now the useis stringently controlled and is being prohibited.

Therefore, there has been proposed a method of cleaning printed circuitor printed wiring boards to remove rosin soldering fluxes which employsa water base composition containing a terpene compound such asd-limonene or diterpene preferably together with a terepene emulsifyingsurfactant, as described in U.S. Pat. No. 4,640,719 to Hayes et al.

It is true that the above composition is effective to remove rosinfluxes or adhesive tape residues from printed circuit boards. But, sincethe terpene compounds used are natural products which are extracted fromorange peel, stable supply thereof is attended at least to an extent bydifficulty, and the quality is not fixed as a further defect. Inaddition, the terpene compounds are usually chemically unstable due totheir rather active unsaturated bonds therein.

It is therefore a general object of the invention to provide a cleaningcomposition which is of high cleaning ability and safety but also ofconstant quality.

It is a further object of the invention to provide a method of removingrosin soldering fluxes, oils, waxes, greasy materials, adhesive taperesiduals or the like from printed circuit boards or printed wiringboards during the fabrication of the boards.

In accordance with the invention, there is provided a cleaningcomposition which comprises dimethylcyclooctadienes.

Further in accordance with the invention, there is provided a method ofcleaning printed circuit boards or printed wiring boards, whichcomprises: contacting the board with a composition comprisingdimethylcyclooctadienes and 2-20% by weight of a surfactant; rinsing theboard with water; and drying the board.

The dimethylcyclooctadienes used as effective ingredients in thecleaning composition of the invention are unsaturated cyclic compounds,but are much more chemically stable than the terpene compounds such asd-limonene. The dimethylcyclooctadienes are industrially prepared bydimerization of isoprene, and available, as industrial products, usuallyas mixtures mainly composed of 2,6-dimethyl-1,5-cyclooctadiene (I) and2,5-dimethyl-1,5-cyclooctadiene (II). ##STR1##

The cleaning composition of the invention may essentially consist of thedimethylcyclooctadienes. When the composition is used as such, after theapplication of the composition to a substrate, the substrate may berinsed with alcohol such as methanol, and then with water, and dried.

The cleaning composition of the invention preferably contains thedimethylcyclooctadienes and a surfactant so that it is removed from asubstrate by rinsing or flushing with water after the application of thecomposition. The surfactant used is not specifically limited, but alkylsulfates, alkyl phenol polyalkylene ethers or sulfosuccinates arepreferably used. More specifically, there may be mentioned, for example,triethanolamine salt of lauryl sulfate, sodium lauryl sulfate or sodiumsalt of synthetic alcohol as alkyl sulfates, ethylene oxide and/orpropylene oxide adduct to nonylphenol as alkyl phenol polyalkyleneethers, and sodium dioctyl sulfosuccinate as sulfosuccinates. Thesesurfactants may be used singly or as mixtures of two or more.

The surfactant may be contained in amounts of 2-20% by weight,preferably in amounts of 5-15% by weight, based on the composition, thebalance being the dimethylcyclooctadienes. However, some of thesurfactants are available as aqueous solutions, so that the compositionof the invention may contain water in a small amount. Further, thecomposition may contain a solubilizer agent such as isopropanols.

The composition of the invention which comprises thedimethylcyclooctadienes and surfactants is especially useful for removalof resin soldering fluxes, oils, waxes, greasy materials, adhesive taperesiduals or the like from printed circuit boards or printed wiringboards during the fabrication of the boards.

The cleaning of printed circuit boards or printed wiring boards with thecomposition of the invention may be carried out in such any known manneras described in before mentioned U.S. Pat. No. 4,640,719. Accordingly,the composition may be applied to boards by immersion in dip tanks or byhand or mechanical brushing. Any of the commercially available printedcircuit cleaning equipment may be utilized. The composition is appliedto printed circuit boards or printed wiring boards usually at roomtemperature for a period usually from one minute to ten minuted,although not limited thereto. The composition may be applied at elevatedtemperatures, if desired.

The composition of the invention is most advantageously employed toremove rosin soldering fluxes from printed circuit boards or printedwiring boards. The baked rosin flux on the boards is put into contactwith the composition for a sufficient period of time to solubilize theflux, followed by removal of the composition from the boards. When thecomposition consists essentially of the dimethylcyclooctadienes, theboards are contacted therewith, rinsed with alcohols and then withwater. When the composition contains a surfactant, the boards may bedirectly rinsed with water to remove the composition therefrom. Afterremoval of the composition as above set forth, the boards are driedwith, for example, nitrogen or the air, to provide boards from which therosin flux has been completely removed therefrom.

As above set forth, the cleaning composition of the invention containsdimethylcyclooctadienes as essential ingredients therein which areindustrially produced using isoprene and are chemically stable, so thatthe composition is suppliable as an industrial product having a fixedquality and a high storage durability. It has a further advantage thatit is capable of being used repeatedly.

Furthermore, the composition of the invention is of high cleaningability, but also rinsed away with water when the composition contains asurfactant, and thus the composition is in particular useful for removalof rosin soldering fluxes from printed circuit or printed wiring boardsduring the fabrication thereof as well as oils, waxes, greasy materials,adhesive tape residuals or the like.

The invention will now be described more specifically with reference toexamples, however, the invention is not limited thereto.

EXAMPLE 1

An amount of 87 parts by weight of dimethylcyclooctadienes, 2.5 parts byweight of an aqueous solution of triethanolamine salt of lauryl sulfate(40% in solid concentration) and 10.5 parts by weight of ethyleneoxide/propylene oxide adduct to nonylphenol were mixed together toprovide a cleaning composition of the invention.

Rosin soldering fluxes as shown in the Table 1 were spin coated over tenseconds at a rate of 1500 rpm on bare silicon wafers, and then baked at300° C. for 30 minutes in an oven.

The wafers thus the fluxes coated and baked thereon were then immersedin the cleaning composition at 25° C. for two minutes in a tank, takenout thereof and rinsed with water, followed by drying with a nitrogengas. The rate of decrease of the flux film was measured with a Dektakapparatus to evaluate flux removal efficacy. The results are shown inthe Table 1.

Meanwhile, the wafers were immersed in the composition at roomtemperature for five minutes, rinsed with water and dried with nitrogen.The wafers were then extracted with a circulating solution of an aqueoussolution of isopropanol, and the resistivity of the solution wasmeasured until equilibrium was reached. The measurements showed that theequivalent NaCl contamination was below 1 μg-NaCl/cm² with respect toall the rosin fluxes shown in the Table 1.

COMPARATIVE EXAMPLE 1

The same wafers as above having the fluxes coated and baked thereon wereimmersed in Freon 113 for two minutes, rinsed with methanol and thenwater. The rate of decrease of the flux film was measured in the samemanner as above. The results are shown in the Table 1.

                  TABLE 1                                                         ______________________________________                                                   Rate of Decrease of Flux Film                                                 (Å/min.)                                                       Rosin Fluxes The Composition                                                                            Freon 113                                           ______________________________________                                        P-550-5.sup.1)                                                                             1584         7750                                                GX-7.sup.1)  8125         9875                                                HI-15.sup.1) 4200         2367                                                PO-4000.sup.2)                                                                             8375         8625                                                ______________________________________                                         Notes:                                                                        .sup.1) Rosin flux from Asahi Kaken K.K.                                      .sup.2) Rosin flux from Senju Kinzoku K.K.                               

EXAMPLE 2

A rosin flux was coated on bare silicon wafers with a soldering iron,and baked at 300° C. for 30 minuted. Then the wafers were immersed inthe same composition as in the Example 1 and Freon 113, respectively, atroom temperature for one minute, followed by rinsing and drying in thesame manner as in the Example 1. The residual amount of the flux on thewafers was measured. The results are shown in the Table 2.

Further, silicone oil was coated on bare silicon wafers with a solderingiron, and then dried. The wafers were then immersed in the samecomposition as in the Example 1 and Freon 113, respectively, at roomtemperature for one minute, followed by rinsing and drying in the samemanner as in the Example 1. The residual amount of the silicone oil onthe wafers was measured. The results are shown in the Table 2.

                  TABLE 2                                                         ______________________________________                                                  Residual Amount (%)                                                           The Composition                                                                          Freon 113                                                ______________________________________                                        Flux        1            1                                                    Silicone Oil                                                                              2            5                                                    ______________________________________                                    

EXAMPLE 3

A device for a socket was mounted on a printed wiring board with astand-off of 0 mm, 0.1 mm, 0.2 mm and 0.3 mm, respectively. The thussurface-mounted board was immersed in the same composition as in Example1 at 30° C. without agitation over a period of 10 minutes. Thereafter,the board was taken out of the composition, rinsed with pure water andultraviolet-dried.

The equivalent NaCl contamination on the surface of the board wasdetermined with an Omega Meter Model 800 (registered trademark of KencoIndustries, Inc., U.S.A.) in accordance with MIL-P-28809A. Thedetermination was also carried out with a board having no socket mountedthereon, namely, a board which had a flux coated and was then dried fortwo days. The results are shown in the Table 3.

                  TABLE 3                                                         ______________________________________                                        Stand-off  Equivalent NaCl Contamination                                      (mm)       (μg/in.sup.2)                                                   ______________________________________                                        0          5.5                                                                0.1        5.1                                                                0.2        5.1                                                                0.3        5.1                                                                (No socket)                                                                              0.0                                                                ______________________________________                                    

EXAMPLE 4

A single drop of a 10% by weight dispersion ofp-octylphenyl-2-chloro-4-(p-heptylbenzoyloxy)benzoate, a liquid crystal,in isopropanol was added to the same composition as in the Example 1.The liquid crystal disappeared in 0.6 seconds.

When Freon 113 was used, the liquid crystal disappeared in 5.3 seconds.

EXAMPLE 5

A plastic specimen (3×50×50 mm) was immersed in the same cleaningcomposition as in the Example 1 at 50° C. for 24 hours. The specimen wasrinsed with water, dried with gauze and increase in weight was measured.The results are shown in the Table 4.

                  TABLE 4                                                         ______________________________________                                                         Increase in Weight                                           Plastics         (% by weight)                                                ______________________________________                                        ABS              0.08                                                         Polyacetal       0.00                                                         Polymethyl methacrylate                                                                        0.00                                                         Epoxy resin      0.00                                                         Polytetrafluoroethylene                                                                        0.00                                                         66-Nylon         0.14                                                         Polycarbonate    0.07                                                         Polybutyl terephthalate                                                                        0.02                                                         Polyethylene terephthalate                                                                     0.00                                                         Polyethylene     0.00                                                         Polypropylene    0.00                                                         Polystyrene      (Dissolved)                                                  Silicone         (Dissolved)                                                  ______________________________________                                    

What is claimed is:
 1. A method of cleaning printed circuit boards orprinted wiring boards, which comprises: immersing the board in acomposition comprising dimethylcyclooctadienes and 2-20% by weight of asurfactant; rinsing the board with water; and drying the board.
 2. Themethod as claimed in claim 1 wherein the dimethylcyclooctadienes aremixtures mainly composed of 2,6-dimethyl-1,5-cyclooctadiene and2,5-dimethyl-1,5-cyclooctadiene. PG,17
 3. The method as claimed in claim1 wherein the surfactant is an alkylsulfate, an alkylphenol-polyalkyleneether or a sulfosuccinate.
 4. The method as claimed in claim 1 whereinthe composition contains a solubilizer.